In a quart-size canning jar or resealable plastic container, add 3½ tablespoons flour and ¼ cup pineapple juice; stir vigorously with chopsticks until combined. Cover with plastic wrap and let rest in a warm spot for 48 hours, opening the jar and stirring again 3 times a day.
Stir in 2 more tablespoons each flour and juice. Cover with plastic wrap and let rest another 48 hours, opening the jar and stirring again with chopsticks 3 times a day. (By the end, you should see some bubbles forming.)
Add 5 tablespoons plus 3⁄4 teaspoon flour and 3 tablespoons tepid filtered water; stir vigorously. Cover and let rest 24 hours.
Add ½ cup flour and 1⁄3 cup tepid filtered water; stir vigorously. Cover and let rest 24 hours. Repeat again the following day. (Starter should be bubbly, cheesy, and smell like beer.) It is now ready to use or give away.
Feed the starter (or advise your friends to) about 8 hours before using: Begin by discarding all but ½ cup starter from the jar. Add ½ cup tepid filtered water and 1 cup total of flours of your choice (a good standard mix is 20% whole wheat, 80% unbleached white). Mix well, scraping down the sides of the jar. To use every or every other day, keep your starter at room temperature and feed it daily. To use intermittently, store in the fridge and feed once a week.